A corner accessory of this type is already known, in particular from document EP 1 178 251, which accessory has one flap carrying on the inside faces of its facing rims studs that engage in oblong circularly-arcuate openings of closed outline that are provided in the facing rims of the other flap.
The flaps are assembled together by squeezing together a little the rims of the flap that include said openings so as to deform them elastically and engage said studs in said openings.
Such an accessory presents several drawbacks.
Firstly, it is difficult to assemble together the two flaps of the accessory since that requires said flaps to be deformed and the studs to be brought into alignment with the respective openings while they are unseen.
In addition, in order to limit the deformation required of the flap including said openings, and thus make the flaps easier to assemble together, the studs provided on the other flap are of small height. Thus, in the event of an impact against said flap, it is easy for the studs to escape from said openings, thereby disassembling the flaps.